“Despite local reductions in pollution and improvement in air quality, it would be irresponsible to downplay the enormous global health challenges and loss of life as a result of the COVID-19 pandemic,” WMO Secretary-General Petteri Taalas said.

“However, now is the time to consider how to use economic stimulus packages to support a long-term switch to more environmentally and climate-friendly business and personal practices.”

A study conducted by Severe Weather Europe says the world typically sees an increase in CO2 emissions in the colder months in the Northern Hemisphere. However, this year has been different.

“We are noticing an interesting development, as the CO2 levels are currently increasing at a much slower rate than expected,” the authors write.

“Looking at the last 12 months of CO2 data from Mauna Loa observatory (in Hawaii), we can see the CO2 rise last year and this season, which shows slower growth than expected.”

Kris Karnauskas, a climate scientist at the University of Colorado Boulder, wrote on Twitter: “I’m not certain this is caused by #COVID19 but there have only been two years since 1975 when CO2 rose less since the first of the year.”

The decline in tourism has brought back “the lagoon waters of ancient times, those of the post-war period, when it was even still possible to bathe in the waters of the canals,” according to local newspaper La Nuova di Venezia e Mestre.

“I guess this is mostly diesel cars out of the road,” Emanuele Massetti, an expert on the economics of climate change at Georgia Tech, told the Washington Post.

One of the largest drops in pollution, The Guardian reports, can be seen over Wuhan, the virus’s epicentre in China.

Wuhan, a city of 11 million people, was put on strict lockdown in January. According to NASA, the nitrogen dioxide levels across eastern and central China have been 10 to 30 per cent lower than normal.

Health officials caution against all international travel. Returning travellers are asked to self-isolate for 14 days in case they develop symptoms and to prevent spreading the virus to others.

Symptoms can include fever, cough and difficulty breathing — very similar to a cold or flu. Some people can develop a more severe illness. People most at risk of this include older adults and people with severe chronic medical conditions like heart, lung or kidney disease. If you develop symptoms, contact public health authorities.

To prevent the virus from spreading, experts recommend frequent handwashing and coughing into your sleeve. They also recommend minimizing contact with others, staying home as much as possible and maintaining a distance of two metres from other people if you go out.